1. Field of the Invention
The present invention relates to a headlight for a motor vehicle, in order to provide a cut-off light beam.
A typical headlight with cut-off light beam comprises:
a collector mirror with an axis;
a source of light placed in the vicinity of the inner focal point of the collector mirror;
a substantially flat bender, the reflective surface of which is oriented towards the interior of the collector mirror, and has an edge which is constituted by a flat curve; and
a lens, situated to the front of the collector mirror and the bender, in order to provide an image of the edge of the bender which defines the cut-off of the beam.
2. Description of the Related Art
In a headlight of this type, the form of the lens is generally determined a posteriori by calculation in order to obtain the light beam required, once the characteristics of the source, the collector mirror and the bender have been determined.
In particular, it is possible to determine the form of the lens section by section, by solving a system of equations for the purpose of optimizing the cut-off profile.
A headlight of this type is known, in particular from the documents FR 2 940 404 and EP 1 610 057, which EP document is equivalent to U.S. Patent Publication No. 2006/0002130 which issued as U.S. Pat. No. 7,682,057, all of which are incorporated herein by reference and made a part hereof, in the name of the applicant company. According to these documents, the lens is determined such as to provide an infinity image from a point of the edge of the bender.
However, all the calculations carried out are based on the hypothesis of use of a localized source of light. In fact it is usual to proceed in this manner, but when the focal point of the collector mirror is small and the source of light is more voluminous, such as, for example in the case of use of a high-power light-emitting diode, it is not uncommon for the focal distance to be of the same order of magnitude as the transverse dimension of the source of light. Significant aberrations then arise, and detract considerably from the quality of the light beam.
This phenomenon occurs more often in the case of a module with a convergent beam.